// Copyright 2014 The Chromium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

#ifndef BASE_ANDROID_APPLICATION_STATUS_LISTENER_H_
#define BASE_ANDROID_APPLICATION_STATUS_LISTENER_H_

#include <jni.h>

#include "base/android/jni_android.h"
#include "base/base_export.h"
#include "base/macros.h"
#include "base/memory/ref_counted.h"
#include "base/memory/singleton.h"
#include "base/observer_list_threadsafe.h"

namespace base {
namespace android {

    // Define application state values like APPLICATION_STATE_VISIBLE in a
    // way that ensures they're always the same than their Java counterpart.
    //
    // Note that these states represent the most visible Activity state.
    // If there are activities with states paused and stopped, only
    // HAS_PAUSED_ACTIVITIES should be returned.
    //
    // A Java counterpart will be generated for this enum.
    // GENERATED_JAVA_ENUM_PACKAGE: org.chromium.base
    enum ApplicationState {
        APPLICATION_STATE_UNKNOWN = 0,
        APPLICATION_STATE_HAS_RUNNING_ACTIVITIES = 1,
        APPLICATION_STATE_HAS_PAUSED_ACTIVITIES = 2,
        APPLICATION_STATE_HAS_STOPPED_ACTIVITIES = 3,
        APPLICATION_STATE_HAS_DESTROYED_ACTIVITIES = 4
    };

    // A native helper class to listen to state changes of the Android
    // Application. This mirrors org.chromium.base.ApplicationStatus.
    // any thread.
    //
    // To start listening, create a new instance, passing a callback to a
    // function that takes an ApplicationState parameter. To stop listening,
    // simply delete the listener object. The implementation guarantees
    // that the callback will always be called on the thread that created
    // the listener.
    //
    // Example:
    //
    //    void OnApplicationStateChange(ApplicationState state) {
    //       ...
    //    }
    //
    //    // Start listening.
    //    ApplicationStatusListener* my_listener =
    //        new ApplicationStatusListener(
    //            base::Bind(&OnApplicationStateChange));
    //
    //    ...
    //
    //    // Stop listening.
    //    delete my_listener
    //
    class BASE_EXPORT ApplicationStatusListener {
    public:
        typedef base::Callback<void(ApplicationState)> ApplicationStateChangeCallback;

        explicit ApplicationStatusListener(
            const ApplicationStateChangeCallback& callback);
        ~ApplicationStatusListener();

        // Internal use: must be public to be called from base_jni_registrar.cc
        static bool RegisterBindings(JNIEnv* env);

        // Internal use only: must be public to be called from JNI and unit tests.
        static void NotifyApplicationStateChange(ApplicationState state);

        // Expose jni call for ApplicationStatus.getStateForApplication.
        static ApplicationState GetState();

    private:
        void Notify(ApplicationState state);

        ApplicationStateChangeCallback callback_;

        DISALLOW_COPY_AND_ASSIGN(ApplicationStatusListener);
    };

} // namespace android
} // namespace base

#endif // BASE_ANDROID_APPLICATION_STATUS_LISTENER_H_
